Degenerative mitral valve disease (DMVD) is a common heart valve disorder in which there is incomplete valve closing, often resulting in shortness of breath, fluid retention, heart failure, and premature death. DMVD is characterized by abnormal connective tissue of the mitral valve, resulting in weakening and rupture of the chordae tendonae (chords), the support structures of the mitral valve, preventing its natural closure. DMVD affects about 2% of the general population and severe, symptomatic DMVD is treated by surgical repair or replacement. Major advances in mitral repair surgery have improved short- and long-term outcomes of patients with this disease. Many such procedures can also benefit individuals having functional mitral valve disease.
Open heart cardiac surgery is highly invasive with a long recovery period, and not well tolerated by elderly or co-morbid patients. Recent innovations in minimally invasive and robotic mitral repair techniques employ sternal sparing approaches to reduce the invasiveness of the procedure, but still require the use of cardiopulmonary bypass which has many associated complications. While the emerging field of transcatheter mitral valve repair avoids the risks of conventional surgery and potentially offers hopes of beating heart mitral valve reconstruction, concerns about residual mitral insufficiency, durability, and inadequate mitral valve repair have been raised.
Devices capable of performing off-pump, mitral valve repair for certain forms of DMVD, such as those disclosed in U.S. Patent Publication Nos. 2008/0188873, 2010/0174297, 2009/0105279 and 2009/0105751, have recently been developed. Such devices can use transapical access to approach and capture the prolapsed portion of the mitral valve leaflet, attach a suture and anchor it at the apex, constraining the flailing leaflet, and eliminating the prolapse. Currently, this procedure relies exclusively on trans-esophageal echocardiography (TEE) guidance in the form of 2D single plane, bi-plane, and 3D imaging. While TEE has thus far proven adequate for the final positioning of the tool and grasping the leaflet, there have been concerns relating to the navigation of the tool from the apex to the target MV leaflet. TEE guidance can be problematic as it may not always be possible to maintain appropriate spatial and temporal resolution in 3D, and it may not always be possible using single 2D and 2D bi-plane views to simultaneously maintain both the tool tip and target site in the field of view. Using 2D echo it also can be difficult to ensure that the tool tip, rather than a cross section of the tool shaft, is visualized. Due to these navigation challenges, the tool can become caught in the region below the valve leaflet, risking leaflet perforation.
After extensive animal studies, the devices described in the above-referenced publications are currently undergoing preliminary in-human trials for the repair of flailing mitral valves. The procedure uses off-pump trans-apical left ventricle (LV) access. Correct leaflet capture is verified using a fiber-optic based detection mechanism. After leaflet capture has been verified, an ePTFE (expanded polytetrafluoroethylene) suture is pulled through the leaflet and the tool is retracted with both ends of the suture. The suture is fixed at the leaflet with a girth hitch knot, adjusted under Doppler echo to ensure minimum mitral regurgitation (MR) and then secured at the apex using a pledget. Multiple neochordae are typically used to ensure optimal valvular function. The single largest problem in navigating the device to the MV target region is that echo imaging must simultaneously keep the target region (MV line of coaptation) and the tool tip in view.
As noted above, traditional approaches for repairing and replacing mitral valves have relied on placing the patient on cardiopulmonary bypass (on-pump) and accessing the arrested heart directly via a median sternotomy. However, because this approach has the potential for major undesired neurological, vascular, and immunological sequalae, there is a push towards performing such procedures in a minimally-invasive fashion. Preliminary experience on animals and humans has indicated that ultrasound guidance alone is often not sufficient for minimally invasive procedures. It would therefore be desirable for a system to provide enhanced surgical guidance in such minimally invasive procedures for repairing patient heart valves.